Objective B-line imaging by lung ultrasound (LUS) is a new tool for evaluating subclinical pulmonary congestion. The aim of this study was to explore the prognostic value of B-line number at admission in predicting symptomatic heart failure (HF) during hospitalization in acute anterior wall STEMI patients. Methods This was a prospective cohort study which consecutively enrolled 96 anterior wall STEMI patients without dyspnea at admission. Pulmonary auscultation, NT-proBNP test, LUS, and echocardiography were performed within 5 hours after primary PCI. Rale occurrence, plasma NT-proBNP levels, B-line number, LVEF, E/e' were recorded, and their predictive value for HF in-hospital was analyzed. Results A total of 19 patients developed symptomatic HF. Median B-line number, NT-proBNP levels, and E/e' in the HF group were higher than those of the nonheart-failure (NHF) group (P 0.001) while LVEF was lower (P = 0.002). There was no statistical difference in rale occurrence between the two groups. Multivariate logistic regression demonstrated that B-lines, E/e', and NT-proBNP independently predicted HF during hospitalization. According to the area under the ROC curve, the strongest predictor is B-lines (0.972), followed by NT-proBNP (0.936) and E/e' (0.928), and combining the three indicators was better than any single parameter (P = 0.048). B-line cutoff >= 18 could well predict HF event with specificity and sensitivity of 94.7% and 94.8%, respectively. Conclusion Subclinical pulmonary congestion reflected by B-lines can independently predict symptomatic HF during hospitalization in patients with anterior wall STEMI, LUS will act as a complementary tool for evaluating cardiac function.